Purification of azo- and azoxybenzene 3,3&#39;,4,4&#39;-tetracarboxylic acid with dioxane and complexes thereof

ABSTRACT

A PROCESS FOR PURIFYING AROMATIC DIANHYDRIDES, IN PARTICULAR AZOBENZENE-3,3&#39;&#39;,4,4&#39;&#39;-TETRACARBOXYLIC ACID DIANHYDRIDE AND AZOXYBENZENE - 3,3&#39;&#39;,4,4&#39;&#39; - TETRACARBOXYLIC ACID DIANHYDRIDE WHICH PROCESS COMPRISES CONTACTING THE DIANHYDRIDE WITH PROCESS COMPRISES CONTACTING THE DIANING THE DIANHYDRIDE DIOXANE COMPLEX SO FORMED TO OBTAIN THE SUBSTANTIALLY PURE DIANHYDRIDE.

United States Fatent C i PURIFICATION OF AZO- AND AZOXYBENZENE 3,3',4,4TETRACARBOXYLIC ACID WITH DI- OXANE AND COMPLEXES THEREOF Maurice Balme,Sainte-Foyles-Lyon, and Bernard Rollet, Lyon, France, assignors toRhone-Poulenc S.A., Paris, France No Drawing. Original application May8, 1969, Ser. No. 823,166, now abandoned. Divided and this applicationDec. 14, 1971, Ser. No. 207,952

Int. Cl. C07c 63/32, 105/00, 107/06 US. Cl. 260-143 7 Cl ABSTRACT OF THEDISCLOSURE A process for purifying aromatic dianhydrides, in particularazobenzeue-3,3,4,4-tetracarboxylic acid dianhydride and azoxybenzene3,3',4,4 tetracarboxylic acid dianhydride which process comprisescontacting the dianhydride with dioxane and isolating and thendecomposing the dianhydride dioxane complex so formed to obtain thesubstantially pure dianhydride.

This is a division of application Ser. No. 923,166 filed May 8, 1969,and now abandoned.

The present invention relates to the purification of aromaticdianhydrides.

Aromatic dianhydrides are useful in the preparation of heatstablepolymers. To obtain high-quality polymers it is necessary to use verypure dianhydrides.

Polyamide-acids obtained by reaction of aromatic dianhydrides withdi-primary diamines in a polar solvent illustrate this point. It has infact been observed that the polyimides obtained by the cyclization ofthe said polyamide-acids possess mechanical thermal properties which arethe better the higher is the intrinsic viscosity of the latter. However,the presence of impurities in the dianhydrides used prevents theattainment of adequately high viscosities.

The aromatic dianhydrides generally obtained by oxidation ofbis-ortho-dialkyl aromatic derivatives have too high an impurity contentto enable them to be used without purification. These impurities mainlyconsist of diacids, triacids and tetraacids and the anhydrides of thediand tri-acids.

French patent specification No. 1,467,485 proposes that thesedianhydrides should be purified by forming addition compounds betweenthem and certain aromatic hydrocarbons. Although the complexes so formedproduce good quality dianhydrides on heating, the yield of thispurification is in general mediocre.

Pyromellitic anhydride has also been purified by recrystallization fromvarious solvents, e.g. acetic anhydride or ethyl acetate. It isdifiicult to adapt such processes to use on an industrial scale becauseof the low solubility on heating of pyromellitic anhydride in thesolvents.

French patent specification No. 1,471,932 describes a process for thepurification of pyromellitic anhydride which comprises washing thepyromellitic anhydride with ketones. However, a large amount of theanhydride becomes dissolved in the ketone used and this therefore meansthat a supplementary recovery operation is necessary.

The present invention provides a process for the purification ofaromatic dianhydrides of the general formula CO 06 o6 in which Rrepresents a tetravalent aromatic radical. The process of the inventiondepends principally on the hither- 3,808,193. Patented Apr. 30, 1974 tounkonwn property of the aromatic dianhydrides of forming complexes withdioxane from which the starting materials may be easily recovered. Theprocess of this invention comprises contacting the dianhydride withdioxane in a heterogeneous phase, and isolating and then decomposing thecomplex so formed to obtain the substantially pure dianhydride.

The tetravalent aromatic radical R can be a mononuclear or a polynucleararomatic radical or a radical consisting of two or more mononuclearand/or polynuclear aromatic radicals linked by valence bonds or throughatoms or radicals. The atoms or radicals which can link these cyclicaromatic systems may be, for example, oxygen, sulphur or phosphorusatoms or alkylene radicals preferably having 1 to 3 carbon atoms, thegroups -fi, -so,-, --N= -r I= 0 o-x-co,

in which Y represents hydrogen, an alkyl radical having 1 to 4 carbonatoms, a cycloalkyl radical or mononuclear or polynuclear aryl radicaland X represents a linear or branched alkylene radical having 1 to 12carbon atoms, a cycloalkylene radical containing 5 or 6 carbon atoms inthe ring, or a mononuclear or polynuclear arylene radical.

The minimum amount of dioxane used is theoretically one molecule foreach dianhydride molecule. In practice it is preferable to use a largeramount of dioxane than this. A large excess is not detrimental to thepurification but to avoid a prohibitive use of the dioxane it ispreferable not to exceed the minimum quantity giving an easily stirredreaction medium.

The aromatic dianhydrides are conveniently mixed with dioxane atordinary temperatures, i.e. 5 to 40 C.; there is generally littleadvantage in exceeding these limits. The mixture is stirred, preferablyin an inert gas atmosphere, for the time necessary for the reaction,which varies according to the aromatic dianhydride purified but isgenerally about 1 to 5 hours.

The complexes thus formed, which are new compounds, can be isolated fromthe reaction medium by centrifugation or by filtration, suction-driedand optionally washed with a little dioxane. They can be obtained in apure state by evaporating the excess dioxane at ordinary temperaturesunder reduced pressure. It should however be pointed out that too low apressure must cause the complexes to decompose. It is important in eachcase to use an optimum pressure, i.e. that which enables the purecomplex to be obtained in minimum time with substantially nodecomposition of the complex. The analysis of these complexes shows thatthey consist of one molecule of aromatic dianhydride and one molecule ofdioxane.

When carrying out the process of this invention it is not necessary toisolate the complexes in the pure state. In general the product obtainedby filtration and optional washing with a little dioxane is directlydecomposed to liberate the purified dianhydrides. This decomposition maybe carried out by heating and/or the application of subatmosphericpressure.

Obviously, the rate of decomposition depends on the nature of thecomplex employed, and the temperature and pressure used. In general therate will be proportionately faster the higher the temperature and thelower the pressure. Therefore, it is not possible to state preciselyoperating conditions which would be applicable to all cases. However,when the dianhydride is pyromellitic anhydride the decomposition iscomplete after 1 hour at C. under atmospheric pressure, is very small at60 C. under the same pressure and in nil after 48 hours at 20 C. under apressure of approximately 10 mm. of mercury. When the dianhydride is theanhydride of azoxybenzene- 3,3',4,4'-tetracarboxylic acid the complexformed is decomposed after 24 hours at 25 C. under a pressure of 1 mm.of mercury.

When decomposition is carried out by heating at atmospheric pressure orunder reduced pressure it is preferable to carry out the operation underconditions which exclude all moisture, e.g. in an atmosphere of a drygas.

The aromatic dianhydrides purified by the new process containpractically no impurities and can be used in the production of excellentquality polycondensates. Thus, when reacted with diprimary diamines theyproduce polyamide-acids, having a high intrinsic viscosity.

The following examples illustrate the invention.

EXAMPLE 1 150 g. of crude pyromellitic dianhydride and 700 ml. of puredioxane are introduced into a 2-liter flask equipped with a mechanicalstirrer, under an atmosphere of nitrogen and at ordinary temperature.The temperature rapidly rises from about 15 to approximately 20 C. andthe mixture thickens. The mixture is stirred for 2 hours 30 minutes,then filtered and the product washed with 4x 125 ml. of dioxane. Thewashed precipitate so obtained is divided.

One-half is placed in a dessicator and dried at ambient temperature (20C.) under a pressure of 1 mm. of mercury for 48 hours. 102.9 g. ofpyromellitic dianhydride/dioxane complex (molecular weight found 306.5;theory 306.2) are so obtained. 70.3 g. of this pyromelliticdianhydride/dioxane complex are maintained at 120 C. under atmosphericpressure for two hours. The loss of weight is 2.98 g. The equivalentmolecular weight of the residue is 218, and it is identified aspyromellitic dianhydride.

The second half is maintained at 120 C. under atmospheric pressure fortwo hours and 73.2 g. of pure pyromellitic dianhydride are obtained.

A polyamide-acid can be prepared from this anhydride in the followingmanner: 250 ml. of dimethylacetamide and 19.02 g. ofbis-(4-aminophenyl)ether are introduced into a 1 liter cylindrical glassreaction vessel under an atmosphere of nitrogen and cooled bycirculating Water at 20 C. After the amine has dissolved 20.73 g. ofpurified pyromellitic dianhydride and 155 ml. of dimethylacetamide areadded. The reaction is exothermic and the temperature rises from about20 to about 25 C. After 2 hours reaction the inherent viscosity of thepolyamide-acid is 1.24 dl./g. (viscosity measured at 25 C. for a 0.5%solution in dimethylacetamide). 0.34 g. of pure pyromellitic dianhydridedissolved in 14.4 ml. of dimethylacetamide are then added. The viscosityrises considerably and after stirring at ambient temperature for 2 hoursa polyamide-acid having an intrinsic viscosity of 2.8 dL/g. is obtained.

EXAMPLE 2 5 00 g. of pure dioxane are introduced into a 1-liter flaskequipped with a mechanical stirrer under an atmosphere of nitrogen, andthen 100 g. of the crude dianhydride of azobenzene 3,3',4,4tetracarboxylic acid are added gradually. When the addition is completethe temperature rises from 29 to approximately 37 C. After stirring thereaction mixture for 2 hours, the precipitate is removed 4 by filtrationand washed with 4x 125 ml. of dioxane. The precipitate is separated intotwo halves. The first half is left in a dessicator at 25 C. under apressure of mm. of mercury until constant in weight; 62.6 g. of complex(molecular weight found 413.6; theory 410.1) are obtained.

The second half is maintained at C. under atmospheric pressure for 2hours and 49 g. of the pure dianhydride ofazobenzene-3,3',4,4-tetracarboxylic acid are produced.

EXAMPLE 3 300 g. of pure dioxane are introduced into a 1-liter flaskequipped with a mechanical stirrer under an atmosphere of nitrogen andthen 100 g. of the crude dianhydride ofazoxybenzene-3,3,4,4'-tetracarboxylic acid are added gradually. Thenfollowing the procedure described in Example 2, 61.6 g. of complex(molecular weight found 427.5; theory 426.1) and 48.9 g. of pureanhydride are obtained.

We claim:

1. An equimolecular complex of dioxane and an arcmatic dianhydrideselected from azobenzene-3,3',4,4- tetracarboxylic acid dianhydride andazoxybenzene-3,3, 4,4'-tetracarboxylic acid dianhydride.

2. A complex according to claim 1 of azobenzene-3,3,4,4'-tetracarboxylic acid dianhydride.

3. A complex according to claim 1 of azoxybenzene-3,3',4,4'-tetracarboxylic acid dianhydride.

4. A process for purifying an aromatic dianhydride selected fromazobenzene-3,3,4,4'-tetracarboxylic acid dianhydride andazoxybenzene-3,3,4,4'-tetracarboxylic acid dianhydride which processcomprises contacting the dianhydride with dioxane in a heterogeneousphase, isolating the complex so formed and then decomposing the latterby heating or the application of subatmospheric gregsure or both, toobtain the substantially pure anhy- 5. Process according to claim 4wherein the dianhydride is the dianhydride ofazobenzene-3,3',4,4'-tetracarboxylic acid.

6. Process according to claim 4, wherein the dianhydride is thedianhydride of azoxybenzene-3,3,4,4'-tetracarboxylic acid.

7. Process according to claim 4, wherein the dianhydride and dioxane arecontacted at a temperature of 5 to 40 C.

References Cited UNITED STATES PATENTS 3,182,073 5/1965 Loncrini260-3463 3,526,618 9/1970 Horstmann et al. 260-452 3,592,827 7/1971Bergman 260-3463 OTHER REFERENCES Farbenfabriken, Chemical Abstracts,vol. 65, 17085 and 17086 (1966).

FLOYD D. HIGEL, Primary Examiner US. Cl. X.R.

26078 R, 78 TF, 152, 208, 346.3

, I UNITED STATES PATEN OFFICE CERTIFICATE OF 'CQRRECTION Patent N0. 3193 Dated April 30. 1 974 Inventor(s) Maurice Balme and Bernard RolletIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, in the heading please insert the priority as follows:-'-Claims priority, application French 151, 198 filed May 9, l968-.

Signed and sealed this 21st day of January 19-75 (SEAL) 'Attestz' McCOYM. GIBSON JR. (3. MARSHALL DANN Attes ting Officer Commissioner ofPatents 7

